The present invention relates to a hydraulic power management system that may be used, for example, in a compact construction vehicle such as a skid steer loader.
Skid steer loaders are typically equipped with a drive and steering system and a main implement, such as a lift arm with a bucket attachment. Hydraulic fluid is provided under pressure to the drive system and to the main implement by way of hydraulic pumps that are driven under the influence of an internal combustion engine.
In many skid steer loaders, the lift arm is raised and lowered under the influence of a lift cylinder, and the bucket is curled and dumped under the influence of a tilt cylinder. The bucket can be replaced or enhanced with various auxiliary implements, such as augers or jack hammers, which provide additional functionality to the skid steer loader. A main valve often controls the supply of hydraulic fluid to the lift cylinder, tilt cylinder, and auxiliary implement in response to actuation of a joystick or other control. In some skid steer loaders, hydraulic fluid from a first hydraulic pump is provided to the lift and tilt cylinders, while hydraulic fluid provided by a second hydraulic pump in addition to the first hydraulic pump is provided to the auxiliary device. In such systems, the pressure and flow of hydraulic fluid provided to the lift and tilt cylinders is often limited to avoid stalling the internal combustion engine. Such pressure and/or flow limitation may be achieved, for example, by using a variable displacement pump, a variable speed drive mechanism, a variable pressure relief valve, or a combination of such devices. However, such systems still may permit the pressure of fluid provided to the auxiliary device to reach levels that would stall the internal combustion engine, for instance, when the operator demands maximum work from the auxiliary implement.